Thank you for visiting nature.com. You are using a browser version with
limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off
compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site
without styles and JavaScript.

Abstract

Marine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost1,2. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes3,4. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat becomes unstable (marine ice-sheet instability) and thus accelerates5. It is thought1,2 that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study1, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth6 and drift direction7. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today8,9, which would produce wide, flat-based plough marks10 or toothcomb-like multi-keeled plough marks11,12. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI13. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers of icebergs smaller than the typical tabular icebergs produced today. Our findings demonstrate the effective operation of MICI in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet.

Kristoffersen, Y.et al.Seabed erosion on the Lomonosov Ridge, central Arctic Ocean: a tale of deep draft icebergs in the Eurasia Basin and the influence of Atlantic water inflow on iceberg motion?Paleoceanography19, (2004)

Acknowledgements

M.G.W. is funded by a UK Natural Environment Research Council (NERC) PhD studentship (LCAG/247 RG72013) held at the Scott Polar Research Institute, University of Cambridge. The OSO0910 expedition with Swedish icebreaker Oden was carried out as collaboration between the Swedish Polar Research Secretariat, the Swedish Research Council, and the US National Science Foundation (NSF). Part of the data shown in Extended Data Fig. 2 was collected on UK NERC-funded cruise JR179.

Search for Julian A. Dowdeswell in:

Search for Martin Jakobsson in:

Search for Robert D. Larter in:

Contributions

J.A.D. and R.D.L. conceived the idea for the study. M.G.W. made the measurements on the multibeam bathymetry data and analysed the results. M.J. was responsible for collection and processing of the IB/RB Oden multibeam bathymetry data. M.G.W. wrote the initial manuscript and all co-authors commented on and provided input to drafts and the final version.

Article Tools

Tools

Share

Editorial Summary

MICI evidence beneath the sheets

In a recent Nature paper, Rob DeConto and David Pollard proposed that a mechanism called marine ice-cliff instability (MICI) could have an important role in the rapid retreat of ice sheets and, potentially, in their collapse. Observational confirmation of MICI has been missing, and the glaciological community has questioned the realism and likelihood of such a mechanism. Now, Matthew Wise and colleagues present an analysis of some plough marks that are approximately 12,000 years old, left by the keels of icebergs in Pine Island Baythe epicentre of modern-day glacial retreat in Antarctica. The authors show that the characteristics of these plough marks are probably explained by MICI, thereby providing an initial confirmation that the mechanism operated in the past, and at a scale that is likely to be relevant to present and future ice-sheet behaviour.